The present invention relates to a plane strain detection apparatus which permits testing samples of soft rock or concrete which have an unconfined compressive strength of less than 35 MPa, under axial loads while continuously monitoring the axial force, axial and lateral displacements and translation of a top support plate supporting the sample.
Biaxial testing of geomaterial, which is defined as including, but not limited to, soil, sand, rock, ceramics, concrete, snow and ice, has been recognized as important in determination of geomaterial characteristics. Patents that describe biaxial geomaterial test systems for soils, etc., include Vardoulakis et al U.S. Pat. No. 4,825,700 and Vardoulakis et al U.S. Pat. No. 4,885,941 which is a continuation of Vardoulakis '700. The Vardoulakis '700 and '941 patents describe a biaxial compression test apparatus for geomaterial samples (for soils, etc.) that is designed to allow shear band formation and provide measurements of the stress displacement characteristics of the failure zone. The geomaterial is formed into a right rectangular prism and is surrounded by a elastomeric membrane and is supported by walls along two parallel faces. An axial load is applied while a bottom support plate is horizontally guided by a linear bearing that is substantially friction free. The surfaces in contact with the specimen are glass lined and lubricated. The load is applied to one end of the specimen and load cells provide accurate measurement of the axial force and any eccentricities thereof, as well as friction along the side walls. Displacement transducers monitor the axial and lateral displacements of the specimen and the horizontal movement of the bottom support plate.